The presence of pharmaceuticals in the environment is an emergent unknown environmental problem, linked to increased production and consumption of pharmaceuticals and, as such, understanding risk perception is fundamental. This study focuses on exploring causes (trust and knowledge) and effects (intention and proper individual disposal of pharmaceutical leftovers) of environmental and health risk perception. Survey data was collected in Portugal, Spain, and France (sample of 509 individuals). Data illustrated that in France, where the quantity of recycled pharmaceuticals is much higher, respondents reported a higher need for knowledge, but not a higher risk perception nor self-reported behaviour. Although previous research illustrates that higher trust correlates with lower risk perception, we found a positive correlation, which highlights the need to comprehend these variables in emergent risks. Results further confirmed a hypothesized moderated mediation model to explain proper disposal behaviour. We found an indirect effect of risk perception on behaviour through intention, which was stronger for participants with higher environmental identity. Understanding the causes and effects of risk perception of pharmaceuticals in the environment thereby contributes to improve pharmaceutical waste management processes and to promote the proper disposal of pharmaceuticals.